1. Field of the Invention
The present invention relates to an image pickup apparatus for generating a color image signal from light incident from a color filter array, to an image signal read method of reading an image signal from the image pickup apparatus, to a computer process method of generating an image signal, to a computer readable storage medium storing programs, to a processing apparatus for obtaining an image signal, and to an image pickup system including the image pickup apparatus and the processing apparatus.
2. Related Background Art
In order to obtain a color image signal in an image pickup apparatus, light is incident upon image pickup elements via a color filter. The color filter includes a primary color filter and a complementary color filter. The primary color filter has three colors, red, green, and blue, whereas the complementary color filter has four colors, cyan, yellow, magenta, and green. A cyan color filter intercepts only red color in the visible light range, a yellow color filter intercepts only blue color in the visible light range, a magenta color filter intercepts only green color in the visible light range, and a green color filter transmits only green light.
In the case of complementary color filters, a luminance signal Y is given by:Y=Ye+G+Cy+Mg  (1),a blue color difference signal is given by:CB=(G+Ye)−(Mg+Cy)  (2),and a red color difference signal is given by:CR=(Cy+G)−(Ye+Mg)  (3)wherein Cy is a signal picked up by image pickup elements via cyan color filters, Ye is a signal picked up by image pickup elements via the yellow color filters, Mg is a signal picked up by image pickup elements via magenta color filters, and G is a signal picked up by image pickup elements via green color filters.
FIG. 1 shows a pattern of color filters according to a first conventional example. This pattern has a periodicity of two pixels in the horizontal direction and four pixels in the vertical direction. With this color filter pattern, the luminance signal Y can be obtained through the equation (1) by using Cy, Ye, Mg, and G in a block of 2×2 pixels, two pixels in the horizontal direction and two pixels in the vertical direction. Similarly the blue and red color difference signals CB and CR can be obtained through the equations (2) and (3) by using Cy, Ye, Mg, and G in the block of 2×2 pixels.
FIG. 2 shows a pattern of color filters according to a second conventional example. This pattern has a periodicity of two pixels in the horizontal direction and four pixels in the vertical direction. With this color filter pattern, the luminance signal Y can be obtained through the equation (1) by using Cy, Ye, Mg, and G in a block of 2×2 pixels, two pixels in the horizontal direction and two pixels in the vertical direction. Similarly the blue and red color difference signals CB and CR can be obtained through the equations (2) and (3) by using Cy, Ye, Mg, and G in the block of 2×2 pixels.
A digital still camera with an image pickup apparatus reads an image at high speed with a sacrifice of resolution before an image is photographed. In accordance with the image signal read at high speed, an image is displayed in a finder such as a liquid crystal finder, an iris is adjusted, a white balance is adjusted, or other preliminary operations are performed. However, with a combination of the color filter layout shown in FIG. 1 and a conventional image pickup apparatus CCD, even if the pixel signal is read at high speed with a sacrifice of resolution by thinning every second pixel in the vertical direction, for example, only cyan and yellow signals are obtained so that the while balance cannot be adjusted in accordance with outputs of the image pickup elements.
Also with the combination of the color filter layout shown in FIG. 1 and a conventional image pickup apparatus CCD, data of two adjacent pixels in the vertical direction is added and thereafter transferred in the image pickup apparatus and output therefrom. Therefore, paired image data is output from the image pickup apparatus. More specifically, referring to FIG. 1, a pair of data of pixels (C1, R1) and (C1, R2) is output, then a pair of data of pixels (C2, R1) and (C2, R2) is output, then pairs of data of column pixels in the rows R1 and R2 are sequentially output. Next, a pair of data of pixels (C1, R3) and (C1, R4) is output, then a pair of data of pixels (C2, R3) and (C2, R4) is output, then pairs of data of column pixels in the rows R3 and R4 are sequentially output. Since these outputs are used, the calculation of the equation (2) can be made, for example, for the rows R1 and R2, but it cannot be made for the rows R3 and R4. Similarly, the calculation of the equation (3) can be made, for example, for the rows R3 and R4, but it cannot be made for the rows R1 and R2. Therefore, the color difference signal for each color can be obtained only from one row among the four rows of image pickup elements so that the resolution of the color difference signal lowers in the vertical direction.
With the combination of the color filter layout shown in FIG. 2 and a conventional image pickup apparatus CCD, a signal read in a high speed read mode can be used for adjusting the white balance.
With the combination of the color filter layout shown in FIG. 2 and a conventional image pickup apparatus CCD, data of two adjacent pixels in the vertical direction is added and thereafter transferred in the image pickup apparatus and output therefrom. Therefore, paired image data is output from the image pickup apparatus. More specifically, referring to FIG. 2, a pair of data of pixels (C1, R1) and (C1, R2) is output, then a pair of data of pixels (C2, R1) and (C2, R2) is output, then pairs of data of column pixels in the rows R1 and R2 are sequentially output. Next, a pair of data of pixels (C1, R3) and (C1, R4) is output, then a pair of data of pixels (C2, R3) and (C2, R4) is output, then pairs of data of column pixels in the rows R3 and R4 are sequentially output. Since these outputs are used, the calculation of the equation (2) can be made, for example, for the rows R1, R2, R3, and R4, but it cannot be made for the rows R5, R6, R7, and R8. Similarly, the calculation of the equation (3) can be made, for example, for the rows R5, R6, R7, and R8, but it cannot be made for the rows R1, R2, R3, and R4. Therefore, the color difference signal for each color can be obtained only from two rows among the eight rows of image pickup elements so that the resolution of the color difference signal lowers in the vertical direction.